WHHIPSNAKE: 75cc Puch Cylinder Project

Hey Gang, Like Alex from 2StrokeStuffing, Kilian Münscher, Doug Binder, Jurrian Mulder & Graham, I am also working on a custom-cast cylinder project. This is not my first, however. I cast a cylinder back in 2009 for the Decepticons ‘No Rules Race’, which was limited to 50cc & built around my Case Reed-Inducted Puch ZA50 motor. -But that’s a story for another time.

Ever since I started goofing with mopeds twenty plus years ago, the Gilardoni 75cc cylinder was the peak of off-the-shelf Puch performance. My second ever build in 2002-2003 was a Gilardoni Puch ZA50. Watching the parts availability flourish over the years from the ‘tractors & volkswagens’ state of things when I started, I’ve been waiting for the Gila’s successor. But it never came. Yes, a Polini ported just so, or a EuroKit / 80 Metra with the right mix of parts will beat a Gila. And of course the watercooled conversions are plain bonkers. But the Gila is still the gatekeeper. So I decided to design and craft a direct replacement for the Gila that outperforms it in every metric. Sure, I do love learning stuff & gaining skills. I have a stubborn DIY, Burt Munro style ethic, but that’s not my goal. The Goal is to beat the Gila. To make a cylinder that slaps onto a bike already set-up for a Gila with power output much more like the AutoScoot, Kart & Dirtbike engines that share many of the same limitations but are significantly punchier than classic mopeds. I recognize that a go-for-broke approach is dumb, and needs to be moderated against the tunability and transmission liabilities of a 40+ year old moped -and yet- I still feel the Gila’s 11-13hp leaves opportunity on the table.

So, I did a buncha of math. Primarily using A. Graham Bell’s  Two-Stroke Performance Tuning (2nd Edition) formulas and parameters. & Honestly, I can’t recommend that book any higher. -But also reverse ‘engineering’ cylinders with performance I’m trying to duplicate: Honda NSR 80, Kawasaki KX85, Malossi MHR series for Dio / Zip / NRG, Aprilia RSA125, Cristofolini, etc..  I landed on some porting numbers I feel are a good starting point.

I then designed a 3D model of the cylinder. Compared to the Gila, I added additional cooling fins, a larger intake system, a larger transfer face and an exhaust flange 1mm wider. The internal port flow is comparable to other modern cylinders. There was a strong emphasis on maximizing port area as well as preferable radial & axial port angles.

Most of the guys previously mentioned are using the lost-PLA method, which (trust me here) is much simpler than lost-wax casting. That process is ^ everything above, but then 3D printing the cylinder with internal structures modelled, adding gates, sprues & runners and then investing the model assembly into plaster. I chose not to go that route because of three reasons: texture, drift & scalability. 3D prints all have a texture, even at a high quality level and I needed the internal face of the transfer ports to have a different texture. Every 3D print I’ve ever worked with, had at least a tiny bit of drift -as in not precisely the shape that was modelled. Since the port features are so small, I needed to really sweat it with my caliper micrometer. Which is not something you can do to a fully formed 3D print. Scalability was also a thought. From experience I knew that it was going to take a few tries to get it perfect and the vendor cost and wait times favored lost-wax casting. Having said all that, there are many penalties to lost-wax and it kinda comes down to individual preference. I trusted my gut.

So I 3D printed the internals of the cylinder as a positive shape (known as a buck in mold-making), I then did some bodywork & sanding to get them exactly right. After that, I created a Silicone RTV mold of these multiple internal parts. This mold is used to cast the internals in plaster. These plaster parts assemble in a modular manner that allows me to make changes without having to redesign / remodel / reprint / remold the entire assembly. This is the pre-fabbed core of the cylinder.

I 3D printed & made a mold of the external cylinder form. The external form has registrations that match the registrations on the pre-fabbed core, so it plugs into the empty mold while waiting for the wax. The external mold was a multi-part assembly to allow for the wax positive to be removed without damage. The mold material is Smooth-On silicone rtv (Mold Max 25) and sometimes TAP Plastic RTV 30. 

After that, I had my wax cylinder loaded with a pre-fabbed plaster core. I then had to attach the sprue, runners, gates, vents, etc… and figure out the best location for these elements as well as a plaster mix that is durable enough but also fluid enough during investing. Pure plaster of paris is way too brittle and will not survive the burnout process, too much sand will cause the investment to freeze quickly and leave voids. I’ll share the recipe if you’re curious. 

I tried a variety of gate, runner & sprue locations -all with mixed results. The textbook method is a sprue that runs alongside the mold down to a gate at the very bottom of the mold, feeding the aluminum up through the bottom. Looking at youtube, some manufacturers simply pour through the center of the cylinder body.  Thus began my campaign of trial and error. Every attempt saw some experimentation with wax type, gate & vent arrangement, and burnout procedure. Across 2019-2020 I attempted around a 12-15 molds & pours with only 3 quality results. Of those 3, one was perfect except it had a tiny imperfection in exactly the wrong spot *rage scream at the sky* and the other two were machinable but very ugly and likely had internal voids. Locating the gates, sprues & runners is tricky but likely not the source of the many failures.

The real culprit here is the burnout process. Once you’ve invested your mold assembly into plaster and the plaster sets, you’ll heat the mold to get the wax (or PLA) out to create the void for the aluminum. Proper burnout is ESSENTIAL. Plaster at the microscopic level is quite porous. While heating the Plaster up, the wax or PLA will start to liquify and soak the plaster. So even if you heat the mold up-side down, to get the wax or PLA to flow out, it’s still soaking into the plaster. If not all of the wax or plaster is eliminated from the plaster during burnout, the hot aluminum entering the mold will cause it to ignite, blowing gas into the void and screw up your casting.

Trust me, I know from experience.

Ideally, you’ll need an electric oven / kiln that can get up to and sustain 800f degrees for days. Professional sculptors I know will burnout 3-4 days prior to pouring aluminum. This would also probably be in a facility that won’t burn your house down. The other thing is that the mold cannot cool down after burnout while waiting for the aluminum. So if you only have the one kiln or furnace, etc.. you're screwed. Also, you can’t burnout the mold one weekend then do the pour the next. Thems the breaks. I tried many different strategies to cheat this and none really worked. 

So I decided to get rid of the wax.

Last winter, in the smoldering aftermath of my most-recent casting failure -and considering the pro & cons of a tricky sandcast system, or a highly expensive tool-steel die-mold process (which is what the factories use), I decided to use the idea of my internal parts plaster mold and expand it to make a multi-part matrix of plaster cores that together, form one fully detailed waxless mold assembly. Without any wax, the prep for the mold is as simple as preheating it to a temperature to drive any moisture out.  

But that meant I had to design a system of plaster chunks that could fit together without altering the original dimensions of the cylinder. So I designed that. It’s an assembly of nine parts (plus the internals) that use the same registrations as the original design. I also tweaked some of the dimensions of the fins & intake tract as I saw opportunities for improvement after the original series.

So I 3D printed all the mold parts, did bodywork & modifications to make them more accurate. I then began the process of making molds for all of the 3D prints. That & living life took about a year. At some point I started calling it the WHHIPSNAKE! because of a funny video about an over-featured piece of equipment. I just recently finished the molds and began pulling plaster cores out last night. They look pretty good & I think it’s gonna work. So that’s everything up to this point, I’ll drop updates as they come up :)

STREET JUSTICE

   A bunch of folks saw the Facebook post, so here's how a rag-tag team of determined goofballs like me recovered (most of) a stolen moped:

   Way back in March, a friend with some Moto experience decided to jump across to the dark murky pit of mopeds. She bought a pretty nice Puch, rode a few weeks and it was promptly stolen off the street outside a bar in a popular nightlife area of town . :( She was pretty pissed and talked to folks all around the area, trying to get info, even putting up flyers looking for the bike. A few interesting conversations occurred but no results. Weeks pass. Like a boss, she promptly buys another (nice, but not as nice as the original) Puch. End of Story? NOPE.

   A weeks ago, an ad pops up on Craigslist advertising Puch Moped Parts. No frame, but an exceptionally coincidental gathering of parts. Sure white bikes exist, with wire wheels and E50's are the norm. But with black covers on both sides of the motor? And the same circuit pipe? And a Polini kit? And the same low bars with the little circle bar-end mirror? No way dude, that's totally her bike.

   The 'tex' number in the ad was bogus, but the email worked. I made contact and got a phone number (burner phone) and talked with a gal about checking it out. She acted like she was talking with someone else in the room. They kept changing times and locations, and given the police's lag time and that the police said the owner herself had to ID the bike (or so we were told), the plan kept falling through. We'd set up a meet and inevitably something would screw it up... Eventually, Louis' roommate also made contact and offered the guy/gal partial trade in weed. This calmed the guy/girl down and we got an address, but the police lag time still messed it up. We tried this at least four separate occasions. The owner also was now directly texting with the thieves trying to set up a meet with them, her and a plainclothes Vancouver PD lieutenant she's buds with. But that fell through and they stopped texting back to her. On Monday, the tweakers re-listed the craigslist ad.

   Throughout this process, factions emerge. Vulcans: We need the owner present to legally ID the bike, then await for Police before any confrontation. (Logic / Rules)  Klingons: Let’s all go over there with baseball bats & fuck ‘em up. *high five* (Brute Force) Yeah, So Louis acts decisively on the Craigslist ad and sets up a meet with the guy. His plan is to get the bike out of the vehicle then confront him to walk away because it’s stolen. No Cops. End of plan. Arthur & I are able to convince him that the guy or guys could be armed, so maybe wait for the cops. This was also a reason previous attempts failed, because they wanted to meet at a residence, potentially full of potentially armed bad dudes. Like a champ, Louis is able to get the guy to meet up at a public space in broad daylight. The new plan: Arthur is a moped Noob looking to buy, Louis is a moped Pro, advising. They will meet with the tweaker/s and stall him/them as long as it takes for Police to show up, with or without the actual owner then we all of us confront tweaker/s.

   What actually happened: Arthur & Louis are waiting near the Mall entrance for guy/s to show up. Jesze is waiting also near the entrance but separately like he doesn’t know them. I’m in the parking lot, very near the parking lot entrance so that I can talk to the cop ASAP when he shows. Tweaker arrives and approaches Jesze, who ignores him, then Louis & Arthur, who then all walk out to the parking lot. The second that happens I call Portland PD, case file number, The owner’s info etc… They don’t want to help, as we’re not the victim, but when I tell the dispatcher it’s happening now, they connect to a cruiser to head our way, looking for ‘Josh with a 65 Barracuda’. The police take FORever. Louis and Arthur are scrutinizing every millimeter of the bike, including the unmolested matching engine VIN. (which is a frame match because it's only had three owners ever!) They do their best, but it’s like 30 minutes they're stalling the guy. I can’t see Arthur & Louis & tweaker from my spot, so Jesze is filing me in over the phone from his better viewpoint.

Arthur was able to snap this candid SpyPhoto of the guy, claiming to be texting his GF.

   Over the phone Jesze says, “ DUDE, we have to go in and snatch the bike NOW!” Arthur I guess was making like he was going to hit the ATM for money and tweaker followed him, leaving Louis with the bike all open out in the parking lot. So I whip the Barracuda around, and Louis, Jesze and I are franticly all tossing bike parts into the backseat. The tweaker comes running up " Hw- what the FUCK?!" . The bike is loaded, so I back up the 'cuda, running into the guy who’s pressed up against it. He turns to Louis, who says “ THIS BIKE IS STOLEN AND WERE TAKING IT WITH US.”…. There’s a small confrontation, but I’m driving away to put distance between the bike (my car) and the tweaker. As I turn the corner to leave the Parking lot, as if on cue the Police car rolls in.

    I wave him down. Me: “Hi, are you here for Josh?” Police: “Are you driving a 65 Barracuda?” (smartass) I quickly explain the situation and he has me roll over to the service ramp by the mall. He calls in a description of the tweaker, who has fled his car and ran into the mall. After exchanging some info, we all head back over to the guys car. More police roll in, they’ve got cops checking the MAX & Bus stops, in the Mall. The first officer takes Jesze, who had his cell camera out during the confrontation like TMZ go identify a guy who matches the description, but it wasn’t him. The car was stolen, and full of stolen stuff, laptops, telescopic photo lenses, clothes, PSU student books etc.. Then a detective guy rolls up and starts CSI-ing the stolen car, after the officer talks with the owner on the phone and more paperwork & BS’ing we all split. Mission Accomplished. Turns out waiting for the owner to ID the bike was optional, kind of a ask for forgiveness, not permission situation …and a little teamwork and persistence gets shit done. The Officer we dealt with told us to 'Keep doing that Street Justice.'

   Looking back at Monday now, it's easy to see some missed opportunities, but it also occurs to me how lucky the group of us got. (Guy was solo, public place, unarmed, no unwanted interference, etc..) It also occurs how capable TEAM JUSTICE was, our ability to form and stick to a plan & then adapt when it was needed. I feel like maybe it couldn't have gone better. I definitely know who I can count on in a squirrely situation. There are various ideas about what happened to the frame. Initially in phone calls it seemed like the frame was available but not included in the photos, as that might be too obvious for anyone who knows the bike. It also may have been sold for scrap. We don't really know. ALSO - everything above is totally from my perspective, it's quite possible I'm remembering wrong, or that useful details are distorted / missing, I certainly wish I was around for the confrontation when the tweaker and the rest of the guys were having at it.

'Piglet' -as rescued from it's thieves.

Vacu-Forming: TRADE SECRETS

If you've read my blog for a bit, or read the Moped Army forums, you may recall that I was producing a clear flywheel cover for the Puch moped. Having gone to school for Industrial Design, I took a section in Vacu-Forming and was able to produce my first flywheel cover specific vacu-former in about a day.

                 It was made out of bondo and masonite primarily. The biggest struggle was removing the formed acrylic off the 'buck'. I tried a number of lubricants and coatings but always ended up prying on the thing and wrecking a few formed pieces in the process. After one frustrating day where I damaged the original,  I began on a totally new vacu-forming rig. The custom buck was cast in a massive block of JB Weld with a wooden core and perforated in key locations to allow for good air flow & forming. The box was made of 3/4in. plywood and the buck sat on a threaded assembly that pulled the buck into the body of the vacu-forming to pop the formed polycarbonate loose. The new rig was an enormous improvement over the first one.

Underside View:

Buck dropping into the Vacu-Former:

The frame that I used to hold the acrylic and then polycarbonate in the oven has been the same since the beginning. It's a modified metal picture frame, even using the original clips to hold the plastic in position. After much experimenting, I devised a metal shield that guided the plastic as it began to soften and expand in the oven's heat.

With formed polycarbonate still attached:

A few weeks ago I was waiting in line at my local TAP Plastic store and thumbing through a book on Vacu-forming and it said something like "Polycarbonate is the most expensive and difficult plastic to Vacuform with the narrowest workable temperature range and prone to failure." and I thought to myself, NO SHIT. Even with a stop watch and digital thermometer Vacu-forming clear plastic is a big ole pain in the dick.

If you have questions about this process, feel free to ask. I probably know more about this junk than any regular person ought to.

Burnout Day

So the Team Nerdspeed support vehicle needed new tires. The day before the new meats were to be attached happened to be MLK jr. Day, so it became Martin Luther Burnout Day. A time of reflection and celebration.



I think Cricket looks very pretty with her new boots.

König 500 GP - Outboard-Powered Underdog

I usually don't do this, but caught this Powerful story and simply HAD to share:

Konig 500 GP

Moped Flamethrower

Still working on jetting the Puch / Swamp Thing. I took a break from that to play with the flamethrower last night. Not fully operational, but a promising start!

A L I V E!